The present invention relates to methods and systems for electronically or computationally transforming individual color components of an image generated by a color video display to correct chromatic aberration associated with an optical system used to view the display.
As used herein, the term "optical system" broadly includes any system in which one or more lens elements are used to form an image. It is well-known that the index of refraction of a lens element varies as a function of the wavelength of light, and that this causes the focal length of the lens element to be wavelength-dependent. This wavelength-dependent variation in focal length is known as the longitudinal chromatic aberration property of the lens element.
It is also well-known that the wavelength-dependent variation in the index of refraction causes a lens element to produce images of different sizes for different wavelengths of light. The difference between the image sizes or heights for different colors is referred to herein as lateral chromatic aberration.
Longitudinal and lateral chromatic aberrations in a lens element can create severe distortions of imagery, especially in the case of a wide angle lens element such as may be advantageously used in a head mounted display ("HMD"). An HMD is an apparatus which typically includes one or more video display devices mounted on a head frame or helmet that is worn by a person who views each display device through a virtual image optical system also mounted on the head frame or helmet. The virtual image optical system expands the field of view subtended by the display devices, thus magnifying the images they generate and providing the viewer with a more compelling feeling of immersion in the imagery. Various types of small, lightweight display devices have been used in HMD's, including monochrome cathode ray tubes ("CRT's"), monochrome and full color liquid crystal matrices, scanned LED arrays and fiber optic rope. Large field sequential full color CRT displays also may be incorporated into an HMD, as is disclosed in commonly assigned co-pending patent application Ser. No. 08/049,563, entitled "Head Mounted Display" and filed Apr. 19, 1993 in the name of Eric C. Haseltine, the disclosure of which is incorporated herein by reference.
Full color video or computer graphics images (e.g., images combining red, green and blue primary colors) generated by display devices having high resolution can provide a person wearing an HMD with a startling illusion of realism. However, chromatic aberration in the optical system through which the display devices are viewed may, along with other types of aberrations (e.g., spherical aberration, coma, astigmatism, field curvature, pin-cushion and barrel distortions), distort the imagery presented to the viewer to the point that the illusion of realism is substantially compromised.
The chromatic aberration properties of a lens element can be corrected. Conventional optical techniques for correcting chromatic aberration usually require the use of additional lens elements to provide achromatic doublet or apochromatic triplet lens combinations. These multi-element optical systems are larger, heavier and more expensive than a single simple positive lens. As a result, such conventional optical correction techniques are not well-suited for use in HMD's and other applications requiring a compact and lightweight optical system.
Various electronic and special image recording techniques which provide compensation for geometric optical distortions in display systems have been disclosed in the prior art, but these techniques have either failed to address the effect of chromatic aberration or do not provide chromatic aberration correction suitable for use with video imagery generated in real time, as would be required for an HMD driven by a computer graphic image generator in a virtual reality entertainment system.
In view of the foregoing, it would be desirable to be able to provide real time chromatic aberration correction for an optical system used to view a color video display, and it would be desirable to be able to provide such correction without requiring a multiple-element lens system or without otherwise adding to the size, weight and cost of the optical system.